Questions about grub2 and UEFI

[castagna]

After a couple of days of googling about it I still have some doubts and I would be quite grateful if anybody
could help me to solve them.

I have a Thinkpad t420s with dual boot (win7 and F15) that I want to upgrade to F16.

Usually when I upgrade I select to custom partition my disk, I keep the ntfs, /usr/local and /home partitions,
and reformat the rest. Then I restore my settings. Since my Thinkpad can use both UEFI and BIOS legacy
I was wondering about the consequences of installing F16. So here you are my questions:

1) The partition schema of my disk is MBR. Did I correctly understood that if I want to use UEFI I have to
pass to GPT?

2) Did I correctly understood that the only way to transform my disk from MBR to GPT is to backup the
partitions I want to save, erase the whole disk, repartition/reformat it, and then restore the saved partitions?

3) Is this worth the effort? That is, what are the advantages of using UEFI over BIOS legacy? Notice that my
disk is a 160Gb SSD, so I do not need terabyte partitions and boot-time is already pretty fast (around 10
secs).

4) If I decide to stick with the MBR disk is there any particular action I should do when doing the custom partition?

5) If I decide to go with GPT / UEFI, same question as the above (I already saw that the instalation guide
states "If your 64-bit x86 system uses UEFI instead of BIOS, you will need to manually create a /boot
partition. This partition must have an ext3 file system. If you choose to partition automatically, your system
will not boot." anything else?


Thank you very much for your help. Since it is the laptop I work every day on, I prefer to play it safe and
avoid to solve my dubts just by trials and errors.

---Beppe---

P.S. Slightly off-topic. I saw in my searches that Thinkpad T(4-5)20 have problems while booting linux with
UEFI. Any more suggestions/references about this specific point?

[srs5694]

1) The partition schema of my disk is MBR. Did I correctly understood that if I want to use UEFI I have to
pass to GPT?

For Windows, yes; Windows ties the partition table type to the firmware type -- MBR only with BIOS and GPT only with UEFI. UEFI itself does not impose such a restriction, and Fedora can install to GPT when using either UEFI or BIOS. (In theory it should be able to install to MBR with either, too, but I've seen some reports that suggest Fedora insists on GPT when using UEFI. I've not looked into this issue myself, though.)

2) Did I correctly understood that the only way to transform my disk from MBR to GPT is to backup the
partitions I want to save, erase the whole disk, repartition/reformat it, and then restore the saved partitions?

That's the way most sources say it must be done, but it's not the only way. My own GPT fdisk (gdisk, cgdisk, and sgdisk) (http://www.rodsbooks.com/gdisk/) utility can do an in-place conversion without data loss (except for BIOS boot loaders, which need to be updated after such a change). I gather there are some Windows utilities that can do this, too, but I've not looked into them.

3) Is this worth the effort? That is, what are the advantages of using UEFI over BIOS legacy? Notice that my
disk is a 160Gb SSD, so I do not need terabyte partitions and boot-time is already pretty fast (around 10
secs).

If you're currently booting Windows in BIOS mode, then switching to UEFI mode will be a big pain, since Windows will no longer boot. There are ways to convert Windows from BIOS to UEFI booting, (https://gitorious.org/tianocore_uefi_duet_builds/pages/Windows_x64_BIOS_to_UEFI) but that's extra effort and risk. There are advantages to UEFI booting, but they're fairly minor. The advantages that spring to mind are:


UEFI booting is likely to be a bit faster.
UEFI boot loaders reside as files in a filesystem, which makes them theoretically easier to maintain than BIOS boot loaders, which live in the MBR, in partitions' boot sectors, and in officially unallocated sectors of a disk. In practice, though, BIOS boot loaders are more mature and better understood than are UEFI boot loaders, which counters this advantage.
UEFI provides more advanced features, such as the ability to load firmware drivers for hardware, which can be useful in some cases.


4) If I decide to stick with the MBR disk is there any particular action I should do when doing the custom partition?

No, at least not if you use BIOS-mode booting.

5) If I decide to go with GPT / UEFI, same question as the above (I already saw that the instalation guide
states "If your 64-bit x86 system uses UEFI instead of BIOS, you will need to manually create a /boot
partition. This partition must have an ext3 file system. If you choose to partition automatically, your system
will not boot." anything else?

UEFI relies on an EFI System Partition (ESP), which is where EFI boot loaders reside. Fedora's installer creates an ESP automatically if you choose automatic partitioning. A separate /boot partition is necessary for GRUB Legacy (which Fedora uses on UEFI installs), but I was pretty sure it was created automatically, at least in the betas. Maybe that's changed with the final release, though.

[castagna]

Dear srs5694,

thanks a lot for your detailed answer, it answered all my doubts. I will stick to MBR and BIOS-mode and leave UEFI for when I change sdd or laptop (next year, probably).

[AdamW]

yep, I'd agree with srs on all counts.

UEFI certainly has a more sane approach to bootloader management, but in practice in most regular use you won't really notice a difference between BIOS and UEFI booting. Once UEFI becomes more widespread it will save us some headaches in dealing with bootloader issues. For Fedora users and most developers it doesn't really have many other practical impacts.